#include <stdio.h>

double fact(int n, int now, double re);

int main()
{
    double sum = 0;
    int n = 0;
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)sum += fact(i,1,1);
    printf("%f\n", sum);
    return 0;
}

double fact(int n, int now, double re)
{
    if(n == 0 || n == 1)return 1;
    re *= now + 1;
    now++;
    if(n == now)return re;
    re = fact(n, now, re);
    return re;
}